This application relates to a method and control of a refrigerant system, wherein normal safe operating limits imposed on a compressor may be temporarily changed to allow for high load operating conditions for a relatively short period of time such as rapid cooldown of a refrigerated container or conditioned space.
Refrigerant systems are known, and typically circulate a first fluid, or so-called primary refrigerant, from a compressor, at which it is compressed, into a first heat exchanger, at which it rejects heat during heat transfer interaction with a second fluid, such as air, and then through an expansion device. The refrigerant is expanded to a lower pressure and temperature in the expansion device, and then passes to a second heat exchanger, at which it accepts heat from a third fluid to be conditioned. Typically, in an air conditioning or refrigeration system, the second heat exchanger is an indoor heat exchanger that will cool air being conditioned and delivered into a climate-controlled environment.
The above is a very simplified description of the operation of a refrigerant system, and many options and more complex arrangements would come within this basic description of a refrigerant system. One feature that is typically associated with most refrigerant systems, and compressors in particular, is safe operating limits imposed on system components. If the safe limits are exceeded for a certain period of time, there is a possibility that the compressor or other system components can be damaged. However, if the system runs only for a short period of time above the safe operating limits and/or these limits are exceeded only slightly, there might be no imminent danger to the system reliability and performance. To determine where the refrigerant system runs, with respect to safe operating limits, certain operational parameters are sensed and transmitted to the refrigerant system control. If those sensed parameters exceed safe limits, then the compressor motor may be shut down, to prevent permanent damage to the compressor.
As an example, if the temperature or pressure at the discharge of the compressor is too high, this could be indicative of a condition at which the compressor could possibly become damaged. Thus, under such conditions, most compressors are provided with a control that would stop operation should preset limits be exceeded. As with most safe limits in industrial applications, the limits are set such that the likelihood of actual damage is very low. That is, if the compressor were allowed to operate just above the established safe limit for a period of time, in the majority of cases, there will not be any damage. Still, the safe limits are important over the life of a refrigerant system to prevent damage to its components, and in a particular, the compressor.
On the other hand, there are times when a compressor would be prone to operate near or above the imposed discharge temperature or pressure safe limits. These conditions may occur, for example, when initially cooling down a climate-controlled environment under high ambient temperature conditions. In the past, when the safe operating limits where exceeded, regardless of the mode of operation or ambient temperature, the amount by which the safe limit is exceeded, or the time the compressor is expected to operate above the safe limit, the refrigerant system was shutdown. The refrigerant system shutdown would often lead to the food spoilage, loss of expensive cargo or prolonged time intervals of discomfort in the conditioned space.